Acids and Bases in Slurries
The use of acids and bases for controlling pH in slurries is widely known. Buffering agents are employed to provide a buffered environment in which moderate amounts of either a strong base or acid may be added without causing any large change in pH. A buffer solution usually contains a weak acid and a salt of the weak acid, an acid salt with a normal salt or a mixture of two acid salts.
Christianson et al., in U.S. Pat. No. 3,661,593, disclose the production of protein concentrates from buffer treated cereal endosperm products. Grinding milling, and air classification are used to prepare the product from the protein that envelopes starch particles in cereal endosperm. Protein is loosened by hydration in an aqueous buffer that typically is isotonic. The isotonic buffer is typically comprised of 0.1M potassium phosphate buffer at pH 7.5 containing 0.006M magnesium chloride.
Patel and Hotaling, in U.S. Pat. No. 3,999,993, disclose a method of buffering rare-earth oxide phosphor slurries to control the pH thereof and thereby retard the formation of undesirable complexes. The process disclosed uses ammonium hydroxide as the buffering agent.
Hans-Heinze et al., in U.S. Pat. No. 4,318,848, disclose a process for the neutralization of basic reaction compositions that uses neutralization by addition of a free surface-active acid. After addition of acid, basic agents are not added or are only added up to a pH value of 3.
In DE 3 119 891 published Dec. 16, 1982, a process for treating fecal sewage is disclosed that is particularly suitable for small plants. Lime, ammonia, or soda is added to the sewage during comminution, in order to obtain a pH of 8-9.
In JP-58-002215 published Jan. 7, 1983, aqueous zeolite slurried are disclosed comprising carboxymethyl cellulose (CMC) as a dispersant and a water soluble alkali metal salt. The slurry is disclosed as being suitable for use as a detergent builder due to its excellent metal ion masking effect, buffer activity under alkaline conditions and a redeposition preventing effect.
Scheffee, in U.S. Pat. No. 4,465,495, discloses a process for making fluid, stable slurries of finely divided coal in water and products thereof, which can be sufficiently highly loaded to serve as a fuel. Use of alkali metal buffer salts to stabilize pH in the 5-8 range is disclosed. Salts such as sodium or potassium phosphate or carbonate, including their acid salts, are used in minor amounts sufficient to provide the desired pH, e.g., about 0.1 to 2% based on the water.
Duminy-Kovarik, in U.S. Pat. No. 4,701,275, discloses an aqueous testing system for testing slurries of magnetic particles, wherein the slurry comprises a buffering element to assist in corrosion resistance. Boric acid buffering is preferred.
Usagawa et al., in EP 0 435 561 A3, disclose silver halide materials containing solid particle dispersions of acidic 2-pyrazoline-5-one based filter dyes. Usagawa et al. teach the addition of small amounts of organic acids, such as acetic acid, citric acid, oxalic acid, and tartaric acid for the adjustment of pH.